The present invention relates to touch sensitive control panels. In particular, the invention relates to capacitive touch sensitive control panels.
Capacitive sensors have become increasingly common and accepted for use in human interfaces and for machine control. In the field of home appliances it is now quite common to find capacitive touch controls operable through glass or plastic panels.
FIG. 1 schematically shows in vertical section a known type of touch sensitive control panel 2 as used in the Monogram™ Model ZISB480DR refrigerator made by the General Electric Company. The control panel 2 comprises a cover plate 4, a sensor-element printed circuit board (PCB) 6 and a control-circuitry PCB 12. The sensor-element PCB 6 has metallic tracks arranged to form touch sensitive areas 8a-c. The configuration of the metallic tracks define the touch sensitive areas of the control panel. The control-circuitry PCB 12 has circuitry for measuring the capacitance of the sensitive areas 8a-8c. The sensor-element PCB 4 is connected to the control-circuitry PCB 12 via wires 14. In FIG. 1, a user's finger 16 is seen approaching the touch sensitive area 8c. The capacitance of the touch sensitive area 8c is modified by the presence of the user's finger. This change in capacitance is measured by the circuitry on the control-circuitry PCB and the user's touch is accordingly identified.
Although not shown in FIG. 1, examples of this type of touch sensitive control panel may include illumination of the touch sensitive areas 8a-8c. This is achieved by providing through-holes in the sensor-element PCB 6 and associated touch sensitive areas 8a-8c through which light from a light-emitting diode mounted on the control-circuitry PCB 12 may pass. The cover plate 4 may include decals identifying particular functions of the touch sensitive areas 8a-8c. 
Variations on this design, such as that shown in by E.G.O. Control Systems GmbH in DE 20119700, are also known in which conductive rubber pillars or helical springs are used to electrically connect the touch sensitive areas adjacent the cover plate and the PCB mounted control circuitry instead of wires. Moreover, in this reference, the touch sensitive areas are provided by a conductive layer printed or deposited on the cover plate, or by a metallic or metallized adhesive foil bonded to the cover plate.
Known types of touch sensitive control panels provide for user interfaces which are subject to a number of limitations. For example, they can be difficult and time consuming to assemble. This is particularly so where a number of separate touch sensitive areas are required, as is often the case. For the example touch sensitive control panel shown in FIG. 1, a separate soldering processing step is required to properly connect the sensor element PCB 6 and the control circuitry PCB 12 together. In the case of known control panels relying on conductive rubber pillars or helical springs, each of the pillars or springs must be carefully attached to a PCB containing control circuitry in proper alignment with the desired touch sensitive areas to which they relate.
In addition, known touch sensitive control panels allow for only a flat touch sensitive surface. This means they can be difficult to incorporate into some devices. This can be because of space requirements, or because a designer wishes to provide a device having a particular overall shape. For example, domestic appliances, such as food blenders, are often too small to provide a sufficiently large flat surface for a suitable control panel. This can be especially so when other aspects of a device's design, for example its ergonomics or overall appearance, need to be considered. It is not generally possible to overlay a conventional flat touch sensitive control panel with a curved cover plate because of the limited sensitivity of the capacitive sensor elements.